This invention relates to hydraulic clutch actuator assemblies for motor vehicle clutches and, more particularly, to a slave cylinder of the so-called xe2x80x9cconcentricxe2x80x9d type having an improved two-piece housing which facilitates the reduction in the size, weight and cost of the overall actuator assembly.
It is known to use a hydraulic actuator assembly consisting of a master cylinder and a slave cylinder to operate the clutch of a motor vehicle. The piston of the master cylinder is mechanically connected to the clutch pedal to move fluid through a conduit through the slave cylinder where a second piston is displaced to operate the clutch. When the pedal is released, bias springs in the clutch force the second piston back to its original position returning fluid from the slave cylinder to the master cylinder.
It is known to design slave cylinders in such a way that they may be concentrically mounted relative to the transmission input shaft within a bell-shaped housing placed between the engine and the transmission. This is generally illustrated for example in assignee""s U.S. Pat. Nos. 4,585,106; 4,585,107; 4,585,108; 4,585,109; 4,609,087; 4,264,290; 4,660,694; 4,684,003; 4,687,084 and 4,708,228.
The housing in the concentric slave cylinder consists generally of two concentric cylindrical portions having a common base flange, in the case of a one-piece construction, or commonly joined base flanges in the case of a two-piece construction. The inner wall of the outer cylindrical portion is spaced from the outer wall of the inner cylindrical portion to define an annular fluid chamber which, when the assembly is completed by addition of appropriate seals, piston and bearing parts, defines the fluid volume for the concentric slave cylinder.
In prior art constructions, the radial dimension of this annular fluid chamber could not be manufactured less than about 6 mm. for one or all of the following reasons. In the case of the two-piece construction, the components were generally made of cast metal with relatively thick wall sections for adequate strength and manufacturability. In the case of a one-piece construction, the annular spacing had to be large enough to permit the entry of a tool to finish the inside surfaces to the degree necessary for proper functioning of seals and bearings.
With a 6 millimeter (mm) radial dimension for the annular fluid chamber of the slave cylinder, and piston and bearing travel; i.e., in the axial direction of the assembly, dictated by mechanical characteristics of the clutch, the overall volume of the slave cylinder annular fluid chamber became relatively large. This of course requires a larger fluid volume in the master cylinder with commensurately larger piston and housing walls as well as increased amounts of hydraulic fluid in the final assembly.
The principal objective of the present invention is to provide a hydraulic actuator assembly for motor vehicle clutches in which the fluid volumes in the master and slave cylinders are significantly reduced and the sizes, weights and manufacturing costs of the master and slave cylinders are commensurately reduced.
In general, this is accomplished by fabricating the concentric slave cylinder housing in two pieces; i.e., an inner cylindrical member having a base flange and an outer cylindrical member having a base flange wherein the annular gap or spacing between the two cylindrical portions when joined is substantially less than 6 mm. and preferably on the order of about 3 or 4 mm.
In one embodiment, the concentric slave cylinder housing includes an inexpensively manufactured stamped steel inner cylindrical member and an injection molded polymer outer cylindrical member joined together by way of overlapping and abutting base flanges. In another embodiment, both inner and outer cylindrical members are manufactured of an injection molded polymer and preferably a reinforced polymer which again are joined by way of overlapping base flanges by conventional methods.
The details of both embodiments are hereinafter described to the degree necessary to permit persons of ordinary skill in the clutch hydraulics technologies to make and use same.